Separation of hydrocarbons



May 13, 1958 Filed March 29, 1955 A. CHAMPAGNAT ET'AL SEPARATION OFHYDROCARBONS 2 Sheets-Sheet 1 ORIFICE- Mlxae DEHYDQATOQ ompncs. 1 [4DEcANTeR 504/ 2 56 DECANTE-R 59 (9 2 3 2. A m m m 75 ELIO ALFPD GwPAaA/AT CHARLES 1 NET BY-W ZZ ms .21

14 TTOF/VEYS SEPARATION OF HYDROCARBONS Alfred Champagnat and CharlesVernet, Paris, France, assignors to The British Petroleum Company,Limited, London, England, a British joint-stock corporation ApplicationMarch 29, 1955, Serial No. 497,642

Claims priority, application France May 19, 1954 17 Claims. (Cl. 196-17)This invention relates to a process for the separation of hydrocarbons.More particularly, the invention relates to a process for the extractivecrystallization of mineral oil fractions, by means of urea.

It is well-known that urea forms crystalline solid adducts with straightchain and slightly branched chain hydrocarbons but does not form solidcompounds with naphthenes, high branched compounds or aromatics. By theuse of urea a method has been developed for refining petroleum fractionsby resolution of the fractions into chemical types by forming the abovesolid compounds, removing the remaining liquid phase (known as the ureaadduction raftinate), decomposing the solid compounds and recoveringfrom the product the liberated hydrocarbons (known as the urea adductionextract).

It is also known that when mixtures of normal parafiins and normalolefins are subject to urea adduction that by reasons of the differentreactivity of these types of compounds towards urea, a degree ofseparation may be ef fected, the parafims tending to pass into theextract and the olefins of similar boiling range tending to pass intothe raifinate. Similarly a degree of separation may be effected betweennormal mono-olefins and normal diolefins, by urea adduction, since theformer compounds tend to pass into the extract and the latter compoundstend to pass into the rafiinate.

Furthermore, it is known that the presence of methanol or other lowmolecular weight alcohols, in admixture with urea and fractionsundergoing treatment, ac-

elerates the rate of formation of the solid derivatives.

it has also been stated in the prior art that mixtures of methanol andwater may be employed as the activating agent.

According to some proposals the urea is employed in solution in asolvent or solvent mixture which, in general, is not miscible withhydrocarbons. Usually, operating in this manner, the solution of ureamust be saturated at the temperature of the reaction with hydrocarbonsand there must be a certain quantity of urea present in addition to thatnecessary for saturation (at the temperature of the reaction), thisexcess urea constituting the available urea for reaction with the normaland slightly branched chain paraflins to produce the solid adduct. Underthese conditions, the reaction between the mixture of hydrocarbons ofthe petroleum fraction to be treated and the urea, partially insolution, gives rise to the formation of a dense slurry comprising anemulsion, generally of the oil in water type, and consisting of acontinuous liquid-phase, comprising the saturated solution of urea, anda discontinuous liquid phase, formed of hydrocarbons that have notreacted with the urea. The emulsion carries in suspension two solidphases, that is, solid adduct crystals and surplus urea crystals whichhave not formed an adduct.

The adduct obtained usually takes the form of a mass of interlacedcrystalline needles, of very large apparent volume. Thus the separationof rafiinate from the thick,

thixotropic complex mixture has been found very diflicult.

In certain processes filtration is used, which leaves on the filter amass of adduct crystals and surplus urea crystals. However, this mass ofcrystals retains a large proportion of rafiinate, which has to beeliminated by washing with the aid of a solvent, if it is desired toobtain a good output and good selectivity in separation. Thesefiltration and washing operations usually call for laborious and costlyapparatusv Other processes have recourse to decantation for separatingthe rafiinate from the aforementioned adduct containing slurry.Nevertheless, this slurry is for the most part very stable and thus,although it is often possible to separate, by simple decantation, amajor proportion of the raffinate, the remainder thereof is retained inthe phase comprising urea solution (which contains also the surplusadduct and urea crystals) thereby adversely effecting the selectivity ofthe process.

Methods for assisting the separation of the raflinate from the slurryare described in the specifications filed in respect to British PatentNos. 704,439 and 716,068. In British Patent 704,439 there is describedthe use of a ternary solvent which is non-miscible with thehydrocarbons, comprising in its preferred form water, methanol anethylene glycol. In Belgian Patent No. 510,286, there is described theoperation of a process using urea containing 0.2 to 5% (preferably 1%)by weight of biuret. The use of this ternary solvent and of ureacontaining biuret permits the formation of crystals of urea and complexof very small dimensions, so that the droplets of raffinate insuspension in the slurry join and are decanted more readily. Alsoaccording to British Patent No. 704,439, when using the ternary solventsdescribed therein, the decantation of the rafiinate is completed by theaddition to the slurry of a small quantity of aqueous methanol derivedby distilling part of the urea solution.

It is an object of the present invention to provide an improved processfor. the extractive crystallization of hydrocarbon mixtures by the useof urea solutions in which the raffinate is separated in convenientmanner from the adduction product. It is a further object to provide aprocess for the separation of normal paraflins from mineral oilfractions. It is a further object to provide a new and useful apparatusfor effecting phase separations.

As hereinbefore described, the complex slurry obtained takes the form ofa thick, thixotropic mass, the thixotropy of the slurry being caused bythe presence in great abundance of the adduct crystals and also by thepresence of crystals of urea in excess of saturation at the operatingtemperature. These adduct crystals and urea crystals have a markedtendency to form, by becoming entangled, suiiiciently solid structuresto offer opposition to the decantation of the droplets of unreactedhydrocarbons (that is, the rafiinate) present in the slurry. It has nowbeen found that under certain conditions as hereinafter described, thesetangled crystalline structures tend to disintegrate, therebyfacilitating the separation of the liquid phases by decantation.

According to the present invention, there is provided a process for theextractive crystallization of a hydrocarbon mixture comprisinghydrocarbons of different chemical type as hereinbefore described, whichcomprises treating said hydrocarbon mixture with a solution comprisingurea whereby there is formed a complex slurry, said slurry consisting ofan emulsion of a liquid phase comprising a urea adduction raflinate anda liquid phase comprising urea solution, said emulsion containing, insuspension, a solid urea adduct with or without solid urea, thereafterseparating at least part of the urea adduction raffinate from thecomplex slurry and prior to and/or during said separation, subjectingsaid slurry to the action of mechanical vibrations whereby there isformed an upper liquid phase comprising rafiinate and whereby the solidmaterials pass into the lower liquid phase comprising urea solution, theseparation of the upper phase being effected by decantation, andthereafter recovering the urea adduction extract from the remainingsolid/liquid phase.

Preferably the process is applied to the treatment of hydrocarbonmixtures comprising normal parafiins in admixture with otherhydrocarbons and wherein the normal paraffins are recovered in theextract. The process of the invention has been found to be particularlysuitable for the treatment of mineral oil fractions, for example,petroleum distillation fractions for the recovery of normal parafiins.

In the decantation stage, wherein the rairinate is separated from theurea solution phase, it has been found that the conditions of vibrationmay be adjusted so as to separate rapidly almost the whole of theraflinate retained by the crystals. A

Preferably the mechanical vibrations imparted to the slurry have afrequency in the range 100 to 2000 per minute. Preferably the amplitudeof said vibrations lie within the range 1 mm. to 5 cms. Moreparticularly it is preferred that the frequency is of the order of 1000per minute and the amplitude of the order of mm.

If desired, the decantation of the raffinate may be carried out in atank equipped with movable bafiles having in association therewith meansfor imparting mechanical vibration to said baffles. Preferably, however,the decantation of the rafiinate is carried out in a tank supported inresilient manner, said tank having, in association therewith, means forimparting mechanical vibration thereto.

Suitably the tank is supported, at least in part by springs. Suitablythe mechanical vibration is imparted by the action of an eccentricallyloaded flywheel.

Preferably the extract hydrocarbons, after separation of the rafiinate,are recovered by heating the urea solution with the adduct held insuspension in order to destroy said adduct, thereby releasing the ureaadducted hydrocarbons and regenerating urea. In this operation thedroplets of raflinate, that had remained fixed to the crystals of theadduct, mix with the hydrocarbons obtained by the destruction of saidadduct. In the treatment of mineral oil fractions, the extract,separated by decantation from the surface of the solution of regeneratedurea, therefore contains some highly branchedchained parafiinhydrocarbons, naphthenes and/or aromatic hydrocarbons, derived fromthese droplets and constituting an impurity in respect of the normalhydrocarbons. When the urea solvent is suitably chosen, the extracthydrocarbons obtained are usually in the form of a mixture of about 70%*normal paraffins and 30% other hydrocarbons. This degree of purity,which is, in general, very much greater than that obtainable by theindustrial separation processes at present in use in the pertoleumindustry, makes possible, according to the invention, the provision offeedstocks for the manufacture of a large number of chemicalderivatives.

According to a further feature of the present invention, a rafiinatefraction having a higher degree of freedom from normal paraffins isobtained. Thus according to this further feature, after separating, withthe assistance of mechanical vibration, the major part of the railinatepresent in the complex slurry, the separated raffinate is also treatedwith a solution comprising urea whereby there is formed a second complexslurry of the type hereinbefore described, the process thereaftercomprises separating the major part of the urea adduction raflinate fromthe second complex slurry and prior to and/or during said separation,subjecting said second slurry to the action of mechanical vibrations ofthe type hereinbefore described.

, According to a still further feature of the presentim.

vention normal paratfins of an improved degree of purity are obtained.Thus according to this further feature, after separating the major partof the urea adduction raiiinate with the assistance of mechanicalvibrations, a quantity of a washing solvent (which is a solvent for theratrinate) is added to the remaining complex slurry. Thereafter asolvent-containing slurry is formed of this mixture by any suitablemethod, such as mechanical stirring.

The stage thus reached is analogous to that which preceded separation ofraiiinate from the complex slurry with the assistance of mechanicalvibrations. Thus the solvent incorporated in the emulsion in the phaseconsisting of urea solution and adduct crystals is separable under thesame conditions as was the rafimate.

Thus the solvent treated slurry containing, in suspension, the solidurea adduct in the presence or absence of solid urea, is treated for theseparation of the major part of the washing solvent from the solventcontaining slurry and, prior to and/or during said separation, theslurry is subjected to the action of mechanical vibrations of afrequency in the range -2000 per minute and of an amplitude of at least1 mm. whereby the solid materials in suspension pass into the lowerliquid phase, comprising urea solution, the separation of the upperphase from the remaining product being effected by decantation, andthereafter the urea adduction extract recovered from the remaining solidliquid phase.

In this manner it is possible to effect a washing treatment upon thecrystals of the complex in suspension in the urea solution. This washingremoves the major part of the microscopic droplets of the rafiinatewhich had not been separated by the first operation of decantation.

A washing solvent can be formed of any suitable mixture of hydrocarbons,but preferably a petroleum fraction is employed. However, as the washingoperation is aimed at increasing the purity of the normal parafiinsresulting from the destruction of the adduct, it is usually desirable toselect a solvent having a distillation range that is distinct from thatof the extract of normal parafiins to be obtained since, after washingthe adduct by the petroleum fraction, and after separating the fractionfrom the remainder of the solvent slurry, microscopic droplets of thissolvent fraction remains fixed to the crystals of the adduct.

During the thermal decomposition of the adduct in suspension in the ureasolution, whereby the extract is freed from urea, the droplets ofsolvent pass into the extract phase and constitute an impurity in thenormal paraflins. When the washing agent used is a petroleum fraction ofdifferent volatility, preferably a fraction that is more volatile thanthe fraction undergoing treatment, the final separation of the smallamount of washing agent retained by the extract is easily achieved bydistillation.

It has been stated that, in general, the process forming the subject ofthe invention yields, on an average, an extract consisting of a mixtureof 70 partsby weight of normal parafiins and 30 parts by weight ofraffinate hydrocarbons. By use of the washing stage hereinbeforedescribed, an extract of even higher normal parafiins content isobtained.

The quantity of petroleum solvent required for the Washing stage isrelatively small and in a petroleum refinery the used washing solvent,together with entrained impurities, may be incorporated in fuels orother commercial products manufactured in the refinery. Alternativelythe impurities may be separated from this washing by solventdistillation.

There is thus achieved, according to the present invention, anextractive crystallization process which may be operated in continuousmanner and which involves the following steps:

(1) Reacting the mixture of hydrocarbons with a urea solution.

(2) Subjectingthe product to mechanical vibration and decanting toremove the raflinate.

(3) Optionally, adding to the remaining phase a washing solventsubjecting the mixture to mechanical vibration' and decanting. to removethe bulk of the washing solvent.

(4) Recovering the extract hydrocarbons, preferably by heating the ureasolution, containing adduct crystals in suspension, to regenerate theurea and release the extract hydrocarbons and separating the extracthydro carbon by simple decantation.

The operation of this process does not necessitate the use of expensiveequipment, such as rotary filters, centrifuges and provides a means ofobtaining, on the one hand, a rafiinate very largely free from normalparaffins and, on the other hand, an extract consisting predominately ofnormal paraflins.

Preferably the process according to the invention is applied to mixtureof hydrocarbons, e. g. petroleum fractions boiling within the range80-350 C.

Preferably there is employed as solvent for urea in the formation ofurea solution, the solvents particularly described in British patentspecification No. 704,439.

Preferably also the urea employed contains 0.2 to 5% .by weight ofbiuret, as described in Belgian patent specification No. 510,286.

The solvent employed for forming the urea solution preferably compriseswater and/or methanol. A particularly suitable solvent comprises a majorproportion of methanol, a minor proportion of water and a'minorproportion of ethylene glycol.

It has been found that best results are obtained by using a solventconsisting of a mixture of 75' parts by weight of 80% methanol and partsby weight of ethylene lycol. Preferably the urea dissolved in thissolvent contains 1% by weight biuret.

it is preferred that the mixing of hydrocarbon feedstock and ureasolution be carried out by pumping these materials in a closed circuitto which feedstock and urea solution are fed at different points on thecircuit and from which the product is withdrawn at a further point onthe circuit. Preferably also, the flow rate (by volume) of circulationof the reactants in the closed circuit substantially exceeds the totalrate of feed of the feedstock and urea solution. Preferably the ratio ofvolume flow rate in the circuit to total volume feed rate of feedstockand urea solution lies in the range 2:1 to 20: Land usually about 10:1,flow rate in the circuit being measured at a point immediately prior tothe take-off point of product. The closed circuit should include a heatexchanger for maintaining the desired reaction temperature. In general,this heat exchanger will function as a cooler.

If desired two or more closed circuits, of the type described above, maybe employed in series for mixing the hydrocarbon feedstock and ureasolution. desired, one or more stirred vessels may be inserted in thelines connecting closed circuits or leading from the final closedcircuit.

Similarly when the process is operated with the inclusion of the step ofwashing the complex mixture remaining after removal of rarfinate, themixing of solvent and urea solution may be carried out in one or moreclosed circuits with or Without the additional use of stirred vessels asdescribed above.

According to one embodiment of the process of this invention, saidprocess comprises fractionally distilling a crude petroleum or apetroleum distillate fraction in a fractionation column with removal ofa side-stream consisting of a relatively lower boiling fraction and withseparate removal of a relatively higher boiling fraction comprisinghydrocarbons capable of separationv by urea adduction, feeding saidhigher boiling fraction to a urea adduction stage wherein saidhydrocarbon mixture is treated with a solution comprising urea wherebythere is formed a complex slurry, said slurry consisting of an emulsionof Also, if

a liquid phase comprising a urea adduction raifinate and a liquid phasecomprising urea solution, saidemulsion containing, in suspension, asolid urea adduct with or without solid urea, thereafter separating atleast part of the urea adduction rafiinate from the complex slurry bydecantation, mixing the remaining complex slurry with a washing solventcomprising at least part of said lower boiling fraction, separating themajor part of the washing solvent from the solvent containing slurry bydecantation, and recovering the extract from the remaining liquid phase,the solvent decanted from the solvent containing slurry being fed backto the fractionating column at a level below that at which the saidside-stream is withdrawn.

Slurry and/or of the solvent from the solvent containing slurry may beassisted by recourse to the method described in the specification of ourcopending British patent. The decantation of the rafiinate and/or of thesolvent is effected by the application, to the mixture prior to orduring separation, of mechanical vibrations as hereinbefore described.

The invention also comprises within its scope the provisionof anapparatus for the resolution, into separate liquid layers, of anemulsion containing a mass of entangled crystals in suspension,-saidapparatus comprising. a vessel having means for the removal of an upperliquid layer, means for the removal of a lower liquid layer and meansfor imparting to said vessel mechanical vibrations having a frequency inthe range to 2000 per minute.

Preferably the apparatus comprises a tank supported in resilient manner,and mechanically associated with an eccentrically loaded flywheelcapable of imparting the said vibrations. Preferably said tank. is.equipped with vertical baffles to increase the overall route to be takenby the urea adduct crystalline mass in its passage through said tank.Preferably the tank has its inlet at one end and itsoutlet at theopposite end, said tank having a rectangular base to which is secured aplurality of parallel vertical bafiles fixed transversally to theoverall direction of flow of the crystalline mass and, alternatingtherewith vertical bafiles attached to the side walls in such mannerthat the crystalline mass is constrained to pass alternately to and fromthe centre line of the tank to increase the overall route to be taken bythe urea adduct crystalline mass in its passage through said tank.

The invention is illustrated but in no way limited with reference to theaccompanying Figures 1-6 wherein:

Figure 1 is a flow sheet of an embodiment of the present invention.

Figure 2 is a plan view of a battle tank serving to separate the crystalslurry from the raflinate.

Figure 3 is a cross section across llilll' of Figure 2.

Figure 4 is an end view of the vat of Figures 2 and 3.

Figure 5 is a cross section of an orifice mixer as used in the apparatusdescribed with reference to Figures 1 and 6.

Figure 6 is a ilow sheet of a second embodiment of the invention.

The circulation schematically represented in Figure 1 is particularlysuitable for separating a petroleum fraction from the normalhydrocarbons and especially front the normal parafiins which itcontains, with for example the production of a heavy kerosene to be usedas fuel in engines working on the principle of jet propulsion. in thatcase the extractive crystallization by means of urea aims atsufliciently lowering the initial temperature of solidification ofkerosene so as toprevent its congelation.

at high altitudes. it is mainly a matter of obtaining a rafiinate ofsutficieutly low congelation temperature, and the by-product of theextractive crystallization in the form of the extract of normalaliphatic hydrocarbons need not be very pure. The invention is-describedhereinafter with particular reference vto the treatment of a petroleum 7fraction boiling in the kerosene range but is clearly in no way limitedto the use of this feedstock.

The kerosene arrives through pipe line 1 and is passed by pump 2 throughpipe line 3 into an apparatus 4 in which it is dehydrated. Apparatus 4may be for example, a salt filter. The kerosene, deprived of its water,arrives through pipe line 5 in the first reaction circuit A. Circuit Acomprises pipe lines 6, 7, 8, 9, and 11; the pump 12 arranged betweenpipe lines 7 and 8 serving to circulate through the various pipe lines:an orifice mixer 13, shown in detail in Figure 5, arranged between pipelines 8 and 9; lastly a cooler 14 arranged between pipe lines 10 and 11.The circuit A is fed with kerosene by pipe line 5, as previouslyindicated, and with a urea solution by pipe line 15. The urea solutionmay be of the kind described in the above mentioned British patent Nos.704,439 and 716,068.

The orifice mixer 13 consists of two flanged tubes 71 and 72. havingbolted, therebetween, an annular plate 73 supporting a concentric tube74 having a number of orifices as illustrated at 75.

The temperature of circuit A is maintained at about to 18 C. by means ofcooler 14 when kerosene is subjected to the treatment. Kerosene and theurea solution arrive at separate points of the circuit A in order toavoid kerosene coming into contact with a fresh solution of urea andthereby preventing the sudden formation of large quantities of adductcrystals with the consequent danger of choking the pipe lines. For thispurpose a pipe line 6 is provided between the points Where pipe lines 5and 15 join the circuit A. Pump 12 disperses the urea solution and thekerosene in the large excess of material circulating in the closedcircuit, thereby producing a thixotropic slurry; the intimate contact isachieved by orifice mixer 13.

The delivery of pump 12 is much greater than the sum of deliveriesthrough pipe lines 5 and 15 feeding into circuit A so that the liquidsintroduced by pipe lines 5 and 15 meet in circuit A considerable excessof slurry containing the adduct already formed. In this manner, aspreviously indicated, the choking of pipe lines is avoided, and anintimate contact and very rapid reaction is achieved.

By pipe line 16 there is withdrawn from circuit A a quantity of slurrycontaining the adduct crystals which is equivalent to the sum of freshkerosene fed throughpipe line 5 and of urea solution fed through pipeline 15.

It should be made clear that the slurry of the adduct consists of aliquid phase, namely the urea solution, in which the adduct crystals,possibly together with crystals of solid urea, are dispersed in greatabundance. In the whole are suspended droplets of unreacted hydrocarbons(urea adduction raflinate). The heterogeneous system is very thick andthixotropic and the interlaced crystals otter mechanical resistance tothe separation by gravity of the droplets of raflinate enclosed withinthem.

The slurry is passed through pipe line 16 to a vibrating decanter Bwhich is shown in more detail in Figures 2, 3 and 4. The decanter Bcomprises a vibrating vat 17 in which are arranged continuous baffles 18by which the slurry is forced to follow a winding path in the directionof the arrows 19 and by which the vibrations to which the vat issubjected are transmitted to said slurry.

As the slurry proceeds through the vat (from left to right in Figures 2and 3) the rafiiuate 20 separates and rises to the surface and iswithdrawn through pipe line 21. The lower phase 22, composed of a slurryof urea solution and suspended adduct crystals, passes into compartment23 and thence to compartment 24 from which it is withdrawn through pipeline 25. The overflow 26 of compartment 23 to compartment 24 isregulated at a fixed height so that a constant level of the surface 27,separating the two phases, is maintained 'at the outlet.

The vibration may be elfected by typical devices, for example by meansof a vibrating platform 28 on which the decanter vat 17 is firmly fixed.This platform 28 is agitated" by vertical springs 29 and horizontalsprings 30 the tension of which may be regulated. The vibrations areproduced by a flywheel 31 provided with an adjustable eccentric loading32. and rotated by a motor 33 with a detachable coupling device 34. Theflywheel 31 rotates at a speed which may be controlled by speedregulator 35; the axle 36 of flywheel 31 is supported by the twobearings 37 and transmits an alternating movement to the vibratingplatform 28. The pipe connections between vibrating vat 17 and the fixedother parts are made by flexible tubings attached to the pipe linesserving for feeding and withdrawal.

It has been established that decantation by a vat such as represented inFigures 2-4 is very elfective. Thus, in general, a residence time ofabout 10 minutes, and often less, in the vibrating vat is suflicient forfreeing the slurry of adduct crystals completely from the mechanicallyseparable rafiinate enclosed therein. This separation is sufiicient ifthe process of extractive crystallization is not intended to produce anextract of normal paratfins of great purity. However, in spite of themost effective decantation by vibration, there always remain microscopicdroplets of raffinate adhering to the adduct crystals in the solution ofurea which cannot be separated by mechanical action. In the description,hereinafter, of the second embodiment of the invention, means forremoving these droplets will be described.

In short, the vibrating decanter B separates theslurry arriving throughpipe line 16 into a raflinate phase which flows through pipe line 21into tank 38, and into a slurry of adduct crystals which leaves bychannel 25.

The raflinate 39, intermediately stored in tank 38, still contains asmall proportion of normal aliphatic hydrocarbons due to the fact thatone reaction stage (circuit A) is insufiicient to completely eliminatethe normal aliphatic hydrocarbons. The raflfinate 39 may be subjected toa second treatment with urea solution. To this end, a pump 40 draws itthrough pipe line 41 to pass it through pipe line 42 into a circuit Cwhich is identical with circuit A and comprises pipe lines 6', 7, 8', 9,10', and 11, a pump 12, an orifice mixer 13, as shown in detail inFigure 5 and cooler 14.

The circuit C is operated in the same manner as circuit A; thehydrocarbons are fed through pipe line 42 and the urea solution by pipeline 43. The slurry of adduct crystals and rafiinate is deliveredthrough pipe line 44. it is advantageous to maintain the reactiontemperature in circuit C slightly lower than that prevailing in circuitA so as to allow those normal paraflins which do not easily combine withurea to form adducts.

The slurry leaving the second circuit C by pipe line 44 passes into asecond vibrating decanter D similar to the vibrating decanter B shown inFigures 24. From the vibrating decanter D a rafiinate phase is withdrawnthrough pipe line 45. The slurry of adduct crystals is withdrawn throughpipe line 46. The raflinate passes through pipe line 45 into a tank 47from which it is withdrawn through pipe line 48. This ralfinate willusually be a kerosene of sutficiently low freezing point for use as fuelin aviation gas turbine engines.

The slurry of adduct crystals fed through pipe line 46, and that fedthrough pipe line 25, are blended in pipe line 49. Pump 50 draws thewhole slurry through pipe line 49 and passes it through pipe line 51 toa steam heater 52 where the temperature of the adduct is raised to about70 C. in order to ensure the decomposition of said adducts and toobtain, on the one hand, an extract phase consisting of straight-chainaliphatic hydrocarbons and, on the other hand, a regenerated solution ofurea. The decomposed adducts are fed through pipe line 53 into decanter54 in which the layers 55 and 56 are formed. The extract hydrocarbons 56are withdrawn by pipe line 57 while the regenerated urea solution 55flows out through pipe line 58 to bedrawn off by pump 59 .by which it ispassed to pipe line 60 and thence to the two pipe-lines and 43, by whichurea solution is fed to the circuits- A and C respectively. I

It may be noted that in the arrangement represented in Figure 1 thehydrocarbon fraction (kerosene) arriving through pipe line 1 is treatedwith urea solution in two stages (circuit A and circuit C). By feedingfresh urea solution into each circuit it is possible to separatefrom thefeed stock the maximum amount of normal parafiins and in consequence toobtain kerosene of the lowest possible freezing point.

With the apparatus represented in Figure l the following results havebeen obtained:

By treating a heavy kerosene, boiling range 200-290 C., with a ureasolution containing, by weight Percent Urea (with 1% of biuret) 42Methanol 33 Ethylene glycol 12.5 Water 12.5

Feed Rafiinate Extract stock S. .G. at C 0.812 0.823 0.779 FreezingPoint (I. P. 16/44) C -27 60 Yield "percent. 75

In Figure 6 is represented a second embodiment of the invention which isparticularly intended to produce normal paraffins of very high purity.In this case the important consideration is not the separation from thefeedstock of the maximum quantity of normal parafiins but rather toobtain normal paraffins of very high purity. To achieve this end adifferent arrangement of the reaction circuits and vibrating decanters,from that hitherto described, is desirable. It is, moreover, desirableto wash the adducts with a solvent which is more volatile than thetreated feedstock. If a kerosene fraction is treated, the reaction andregeneration may be carried out at the temperatures described withreference to the plant illustrated in Figure 1.

Kerosene is fed through pipe line 101 by pump 102 and thence throughpipe line 103 and a dehydration device 104 such as a salt filter. Thedry kerosene is then introduced by pipe line 105 into a first reactioncircuit A, similar to circuit A of Figure 1, comprising in addition topipes 106, 107, 108, 169, 110, and 111, a pump 112, an orifice mixer 113(as illustrated in Figure 5) and a cooler 114. The urea solution is fedto the circuit A through pipe line 115 and thus enters circuit A at aseparate point from the kerosene. The slurry formed in the first circuitA is passed through pipe line 116 into a second circuit C, identicalwith circuit A, containing pipes 106', 107, 108, 109', 110, 111, pump112, an orifice mixer 113 (as illustrated in Figure 5) and cooler 114.The purpose of this second reaction circuit C is to complete thereaction started in the first circuit A at a slightly lower temperature.

The procedure differs from that described with reference to Figure l inthat the whole urea solution is passed into the first reaction circuit(circuit A) and that the raffinate and the slurry of complex crystalsare not separated between the first circuit A and the second circuit C.v

The slurry formed by the reaction in circuit C is passed through pipeline 110 and stirred vessel 179 into the vibrating decanter B of thetype previously described with reference to Figures 2-4. The rafiinate120 decantedfrom the surface-overflows through pipe 1ine-121 into tank138. The slurry of adduct crystals which-still contains a small quantityof raffinate is takenthrough pipe line and pump 161 which also receivesthrough pipe line 162 a washing solvent which is more volatile than thetreated kerosene. The mixture of the slurry'of adduct crystals and thewashing solvent is driven through pipe line 163 in the orifice mixer 164which is similar to the devices 13, '13, 1-13 and 113 used in thereaction circuits. This device 164 efiects an intimate contact betweenthe solvent (arriving through pipe line 162) and the adduct arrivingthrough pipe line 125. The slurry, which now contains the solvent,overflows through "pipe line 144 into the vibrating decanter D which issimilar to decanter B.

At the upper part, the solvent charged with the ratfinate extracted fromthe slurry of adduct crystals flows through pipe line 145 into the tank147 for spent solvent. The washed slurryleaves-device D through pipeline 146 and is taken by pump 150 to be passed through pipe line 151 tothe steam heater 152 where itis heated to 70 C. and the adducts aredecomposed into an extract phase (straight-chain aliphatic hydrocarbons)and a phase comprising the solution of urea. This mixture passes throughpipe line 153 into decantation vat 154. The regenerated urea solution155 is drawn by pump 159 through pipe line 158 and passedinto pipe line115 mentionedabove which feeds the first reaction circuit A.

The extract phase 156 from tank 154 is passed through a pipe line 157 toan intermediate tank from where the extract containing a small quantityof solvent which had not been removed in the vibrating decanter D ispassed through pipe line 166 and pump 167 to a steam heater 168 followedby a distillation column 169. The extract, deprived of solvent, leavesat the bottom of the column through pipe line 170. This extract isstored in a tank 171 from which it is taken by pipe 1ine 157.

Solvent vapours are withdrawn from the top of column 169 by pipe line172 and condensed in condenser 173. The recovered solvent is passed bypipe line 174 to the storage tank 175. I

Likewise, the spent solvent from tank 147 containing ratfinate is drawnby pump 167 through pipe line 166 and passed for distillation into steamheater 168' followed by column 169. The recovered raftinate leaves atthe bottom of the column through pipe line 176 to arrive in therafiinate tank 138 from which the raftinate may be withdrawn throughpipe line 148.

The'solvent vapors leave at the top of the column through pipe line 172to be condensed in the condenser 173. The liquid solvent is passedthrough pipe line 174' to a storage tank'175. From tank 175 solvent ispassed by pipe line 178 and returned to circulation by pipe line 162.

It will be apparent that the apparatus described by reference to Figures1 and 6 each comprise the same number of reaction circuits (A and C forFigure 1, A and C for Figure 6) and the same number of vibratingdecanters (B and D'inthe case of Figure 1, B and D in the case of Figure6). The equipment for the regeneration of the urea solution isidentical. It is thus possible to employ the same equipment withsuitable connections to operate either of the embodiments illustrated inFigures 1 and 6.

'It is also clear that it is possible to add one or several vibratingdecanters to produce either normal parafiins of increased purity or toobtain, at the same time, a raffinate completely deprived of normalparafiins.

In a petroleum refinery the redistillation of solvent may be carried outby passing the spent (raftinate containing) solvent coming from pipeline 166' to the principal column of the atmospheric distillation unit(replacing column 169) under the conditions set forth above. Freshsolvent is then withdrawn continuously from the 11 light distillateleaving the column to be passed into tank 175.

The invention is illustrated further but in no way limited withreference to the following examples. The frequency of vibrationsimparted to vibrating tanks was 1000 per minute, the amplitude being 10mm.

Example 1 The urea solution employed had the following composition,parts being by Weight: Urea, containing 1% of biuret 42%; methanol 33%;ethylene glycol 12.5%; water 12.5%.

With the apparatus illustrated in Figure 5 the following results wereobtained in the treatment of a kerosene of The apparatus used was asdescribed with reference to Figure 5 with the following modifications:

(a) Solvent Washing was carried out using two vibrating decantingvessels, solvent being passed back in countercurrent flow from thesecond vessel to the first vessel.

(b) Solvent recovery was elfected in a refinery atmospheric distillationunit.

The feedstock to the process was a gas oil derived from Middle Eastcrude oil processed under the conditions and with the results shown inthe following tables. Proportions are expressed as vol. percentages onfeed. I Reaction stage:

Urea solution fed percent 240 Concentration of urea solution ingrams/litre 405 Saturation temperature of the urea solution C 38 Finalreaction temperature C 28 Reaction tim minutes 60 Temperature C 28Decantation stage:

Time taken for decantation r minutes 12 Recovery of raflinate percent 85Washing stage:

Washing solvent fed do 50 Decomposition stage:

Temperature of eifecting decomposition of the adduct C 70 Time taken fordecomposition of the adduct minutes 30 Distillation stages:

Feed of fat solvent to the distillation for removal of extract percent2.5 Feed of fat solvent to the atmospheric column for removal ofraiiinate percent 52.3 Composition of fat solvent- Lean solvent do 47.5Raifinate do.. 4.8 Yield of extract do 10 INSPECTION DATA F RECOVEREDEXTRACT HYDRO- CARB NS Density at 20/4 C 0.770 Distillation A. S. T. M.:

Initial boiling point C 242 C 251 50% C 262 95% C 291 Final boilingpoint C 303 Refractive index at 20/13 C degrees 1.433 Viscosity at 20 Ccentistokes 3.8 Flashpoint (closed) C 93 12 Freezing point C +7 Anilinepoint C 92 Aromatic content percent by vol Less than 0.5 Total sulphurpercent by weight 0.004 Number of carbon atoms/molecule 13-17 Degree ofpurity of normal paraflins percent vol 96 We claim:

1. A process for the extractive crystallization of a hydrocarbon mixturecomprising hydrocarbons which form adducts with urea and hydrocarbonswhich do not form adducts with urea, which comprises treating saidhydrocarbon mixture with a solution comprising urea dissolved in asolvent whereby there is formed a complex slurry, said slurry comprisinga liquid phase comprising a urea adduction raifinate, a liquid phasecomprising urea solution, and, in suspension, a solid urea adduct,thereafter separating at least part of the urea adduction raflinate fromthe complex slurry by decantation and within the period prior to andduring said separation, subjecting said slurry to the action ofmechanical vibrations of an amplitude in the range of 1 mm. to 5 cms.and a frequency in the range of 100-2000 per minute whereby there isformed an upper liquid phase comprising raifinate and whereby the solidmaterials pass into the lower liquid phase comprising urea solution, andafter said separation recovering the urea adduction extract from theremaining mixture of solid and liquid phases.

2. A process as specified in claim 1 in which urea adduction extract isrecovered from the remaining mixture of solid and liquid phases byheating said mixture whereby the urea adduct is decomposed, andthereafter separating a phase comprising urea adduction extract from aphase comprising urea solution.

3. A process as specified in claim 1 in which the slurry formed bytreating the feedstock with a solution comprising urea dissolved in asolvent is separated by decantation while subjecting said slurry tomechanical vibrations of a frequency in the range about 1000 per minuteof an amplitude of about 10 mm.

4. A process as specified in claim 1, for the recovery of a rafiinate oflow normal paratlin content, which comprises further treating the upperphase, separated by decantation, with a solution comprising ureadissolved in a solvent whereby there is again formed a complex slurry,said slurry comprising a liquid phase comprising a urea adductionrafiinate, a liquid phase comprising urea solution, and, in suspension,a solid urea adduct, thereafter separating at least part of the ureaadduction raiflnate from the complex slurry by decantation and, withinthe period prior to and during said separation, subjecting said slurryto the action of mechanical vibrations of an amplitude in the range of 1mm. to 5 cms. and a frequency in the range of 1002000 per minute wherebythere is formed an upper liquid phase comprising ralfinate and wherebythe solid materials pass into the lower liquid phase comprising ureasolution, and, after said separation, recovering urea adduction extractfrom the remaining mixture of solid and liquid phases.

5. A process as specified in claim 1 which comprises mixing the mixtureof solid and liquid phases, which remains after decantation of the upperphase, with a washing solvent, separating by decantation the major partof the washing solvent from the solvent containing slurry so formed andprior to within the period prior to and during said separation,subjecting the slurry to the action of mechanical vibrations in therange 100 to 2000 per minute and of an amplitude in the range 1 mm. to 5ems. whereby the solid materials in suspension pass into the lowerliquid phase, comprising urea solution, and after said separationrecovering the urea adduction extract from the remaining mixture ofsolid and liquid phases.

6. A process as specified in claim 5 in which the mixture of solid andliquid phases recovered after separation 13 of solvent is subjected toheat treatment, whereby the urea adduct is decomposed, thereafterseparating a phase comprising urea adduction extract from a phasecomprising urea solution.

7. A process as specified in claim in which the washing solvent is apetroleum distillate fraction.

8. A process as specified in claim 1 in which the hydrocarbon mixtureundergoing treatment is a petroleum distillation fraction.

9. A process as specified in claim 8 in which the petroleum distillationfraction has an initial boiling point above 80 C. and a final boilingpoint below 350 C.

10. A process as specified in claim 1 in which the solution comprisingurea dissolved in a solvent is formed by dissolving urea in a solventcomprising methanol.

11. A process as specified in claim 1 in which the solution comprisingurea dissolved in a solvent is formed by dissolving urea in a solventcomprising a major proportion of methanol and minor proportions of waterand ethylene glycol.

12. A process as specified in claim 1 in which the solution comprisingurea dissolved in a solvent is saturated at the temperature of treatmentwith the hydrocarbon mixture.

13. A process as specified in claim 1 in which the urea solutioncomprises a small proportion of biuret.

14. A process as specified in claim 13 in which the amount of biuretemployed constitutes 0.25.0% by weight of the urea.

15. A process as specified in claim 1 in which the hydrocarbon feedstockand solution comprising urea are mixed by pumping in a closed circuit,to which feedstock and the solution comprising urea dissolved in asolvent are continuously fed at different points on said circuit andfrom which product is continuously Withdrawn at a further differentpoint.

16. A process as specified in claim 15 in which the volume flow rate ofcirculation of reactants in the closed circuit substantially exceeds thetotal rate of feed of the hydrocarbon feedstock and solution comprisingurea dissolved in a solvent.

17. A process as specified in claim 15 in which the hydrocarbonfeedstock and solution comprising urea dissolved in a solvent are mixedin a plurality of closed circuits connected in series.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR THE EXTRACTIVE CRYSTALLIZATION OF A HYDROCARBON MIXTURECOMPRISING HYDROCARBONS WHICH FORM ADDUCTS WITH UREA AND HYDROCARBONSWHICH DO NOT FORM ADDUCTS WITH UREA, WHICH COMPRISES TREATING SAIDHYDROCARBON MIXTURE WITH A SOLUTION COMPRISING UREA DISSOLVED IN ASOLVENT WHEREBY THERE IS FORMED A COMPLEX SLURRY, SAID SLURRY COMPRISINGA LIQUID PHASE COMPRISING A "UREA ADDUCTION RAFFINATE, A LIQUID PHASECOMPRISING UREA SOLUTION, AND, IN SUSPENSION, A SOLID UREA ADDUCT,THEREAFTER SEPARATING AT LEAST PART OF THE UREA ADDUCTION RAFFINATE FROMTHE COMPLEX SLURRY BY DECANTTATION AND WITHIN THE PERIOD PRIOR TO ANDDURING SAID SEPARATION, SUBJECTING SAID SLURRY TO THE ACTION OFMECHANICAL VIBRATIONS OF AN AMPLITUDE IN THE RANGE OF 1 MM. TO 5 CMS.AND A FREQUENCY IN THE RANGE OF 100-2000 PER MINUTE WHEREBY THERE ISFORMED IN UPPER LIQUID PHASE COMPRISING RAFFINATE AND WHEREBY THE SOLIDMATERIALS PASS INTO THE LOWER LIQUID PHASE RECOVERING UREA SOLUTION, ANDAFTER SAID SEPARATION RECOVERING THE UREA ADDUCTION EXTRACT FROM THEREMAINING MIXTURE OF SOLID AND LIQUID PHASE.